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Full text of "Handbook Of Chemical Engineering - I"

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MECHANICAL SEPARATION
269
beating engine has consequently a bad effect upon the fiber. The gum can be removed if the plants are steeped immediately after cutting them down. After the gum has become hardened caustic soda is required to remove it, and this chemical has an injurious effect on the fiber.
In the decortication of grains the cortex or bran can be removed by abrasion. The devices used for this purpose are commonly double roughened cones, the arrangement of cones being about the same as in an ordinary coffee grinder. Pearl barley is prepared by machines of this kind. It has been stated that the Romans were familiar with the decortication of grain by grinding it in a mortar with abrasive grains and the coats of any cereal can be removed by mill stones, the upper stone
FIG. 5.—Federal-Esperanza classifier.
being held high enough to avoid crushing the cereal. Oats are commonly hulled in this way. Corn for hominy can be hulled by steeping in weak caustic potash followed by thorough washing. The coats are readily loosened by this treatment.
SEPARATION OF SOLIDS FROM LIQUIDS.   LIQUIDS FROM LIQUID
The separation of coarse solids from water and other liquids can best be done with revolving screens if the least loss of head room is required. If loss of head room be not a consideration inclined stationary screens may be used. A convenient form of this kind is the catenary screen. To work out the curve of the supports for this screen, bend to a right angle a piece of screen cloth with mesh opening small enough to prevent passage of solids. Tack to either end of the bent screen a piece of thin board, forming a trough. Rest this device on a support with the angle of the screen down and the legs of the triangle projecting up into the air and firmly held by blocks placed under them. The solids with the operating proportion of water is discharged into the device